In Situ Electrochemically Derived Amorphous-Li2 S for High Performance Li2 S/Graphite Full Cell

Air-Stable Li2S Cathodes Enabled by an In Situ-Formed Li+ Conductor for Graphite-Li2S Pouch Cells

Using Li2S cathodes instead of S cathodes presents an opportunity to pair them with Li-free anodes (e.g., graphite), thereby circumventing anode-related issues, such as poor reversibility and safety, encountered in Li-S batteries. However, the moisture-sensitive nature of Li2S causes the release of hazardous H2S and the formation of insulative by-products, increasing the manufacturing difficulty and adversely affecting cathode performance. Here, Li4SnS4, a Li+ conductor that is air-stable according to the hard-soft acid-base principle, is formed in situ and uniformly on Li2S particles because Li2S itself participates in Li4SnS4 formation. When exposed to air (20% relative humidity), the protective Li4SnS4 layer maintains its components and structure, thus contributing to the enhanced stability of the Li2S@Li4SnS4 composite. In addition, the Li4SnS4 layer can accelerate the sluggish conversion of Li2S because of its favorable interfacial charge transfer, and continuously confine lithium polysulfides owing to its integrity during electrochemical processes. A graphite-Li2S pouch cell containing a Li2S@Li4SnS4 cathode is constructed, which shows stable cyclability with 97% capacity retention after 100 cycles. Hence, combining a desirable air-stable Li2S cathode and a highly reversible Li-free configuration offers potential practical applications of graphite-Li2S full cells.

Nanostructured Li2S Cathodes for Silicon-Sulfur Batteries

Lithium-sulfur batteries are regarded as an advantageous option for meeting the growing demand for high-energy-density storage, but their commercialization relies on solving the current limitations of both sulfur cathodes and lithium metal anodes. In this scenario, the implementation of lithium sulfide (Li2S) cathodes compatible with alternative anode materials such as silicon has the potential to alleviate the safety concerns associated with lithium metal. In this direction, here, we report a sulfur cathode based on Li2S nanocrystals grown on a catalytic host consisting of CoFeP nanoparticles supported on tubular carbon nitride. Nanosized Li2S is incorporated into the host by a scalable liquid infiltration-evaporation method. Theoretical calculations and experimental results demonstrate that the CoFeP-CN composite can boost the polysulfide adsorption/conversion reaction kinetics and strongly reduce the initial overpotential activation barrier by stretching the Li-S bonds of Li2S. Besides, the ultrasmall size of the Li2S particles in the Li2S-CoFeP-CN composite cathode facilitates the initial activation. Overall, the Li2S-CoFeP-CN electrodes exhibit a low activation barrier of 2.56 V, a high initial capacity of 991 mA h gLi2S-1, and outstanding cyclability with a small fading rate of 0.029% per cycle over 800 cycles. Moreover, Si/Li2S full cells are assembled using the nanostructured Li2S-CoFeP-CN cathode and a prelithiated anode based on graphite-supported silicon nanowires. These Si/Li2S cells demonstrate high initial discharge capacities above 900 mA h gLi2S-1 and good cyclability with a capacity fading rate of 0.28% per cycle over 150 cycles.

Hard Carbons for Use as Electrodes in Li-S and Li-ion Batteries

Activated hard carbons, obtained from the pyrolysis of various waste biomasses, were prepared and characterized for use as the active material for the fabrication of battery electrodes. The preparation consisted of a pyrolysis process, followed by an activation with KOH and a further high-temperature thermal process. TG and DTA were used to discriminate the steps of the activation process, while SEM, XRD, and Raman characterization were employed to evaluate the effects of activation. The activated carbons were tested as electrodes in lithium-sulfur and lithium-ion batteries. The carbonaceous materials coming from cherry stones and walnut shells have proved to be particularly suitable as electrode components. When used as anodes in lithium-ion batteries, both carbons exhibited a high first cycle discharge capacity, which was not restored during the next charge. After the first two cycles, in which there was a marked loss of capacity, both electrodes showed good reversibility. When used as cathodes in lithium-sulfur batteries, both carbons exhibited good catalytic activity against the redox reaction involving sulfur species with good cycle stability and satisfactory Coulombic efficiency.

Lithium Sulfide as Cathode Materials for Lithium-Ion Batteries: Advances and Challenges

Due to the ever-growing demand for high-density energy storage devices, lithium-ion batteries with a high-capacity cathode and anode are thought to be the next-generation batteries for their high energy density. Lithium sulfide (Li2S) is considered the promising cathode material for its high theoretical capacity, high melting point, affordable volume expansion, and lithium composition. This review summarizes the activation and lithium storage mechanism of Li2S cathodes. The design strategies in improving the electrochemical performance are highlighted. The application of the Li2S cathode in full cells of lithium-ion batteries is discussed. The challenges and new directions in commercial applications of Li2S cathodes are also pointed out.