Thick free-standing electrode based on carbon-carbon nitride microspheres with large mesopores for high-energy-density lithium-sulfur batteries

The development of sulfur cathodes with high areal capacity and high energy density is crucial for the practical application of lithium-sulfur batteries(LSBs).LSBs can be built by employing(ultra)high-loading sulfur cathodes,which have rarely been realized due to massive passivation and shuttling.Herein,microspheres of a carbon-carbon nitride composite(C@CN)with large mesopores are fabricated via molecular cooperative assembly.Using the C@CN-based electrodes,the effects of the large mesopores and N-functional groups on the electrochemical behavior of sulfur in LSB cells are thoroughly investigated under ultrahigh sulfur-loading conditions(>15 mgS cm^(-2)).Furthermore,for high-energy-density LSBs,the C@CN powders are pelletized into a thick free-standing electrode(thickness:500^m;diameter:11 mm)via a simple briquette process;here,the total amount of energy stored by the LSB cells is 39 mWh,corresponding to a volumetric energy density of 440 Wh L-1 with an areal capacity of 24.9 and 17.5 mAh cm^(-2) at 0.47 and 4.7 mA cm^(-2),respectively(at 24mgS cm^(-2)).These results have significantly surpassed most recent records due to the synergy among the large mesopores,(poly)sulfide-philic surfaces,and thick electrodes.The developed strategy with its potential for scale-up successfully fills the gap between laboratory-scale cells and practical cells without sacrificing the high areal capacity and high energy density,providing a solid foundation for the development of practical LSBs.

Electrocatalytic and stoichiometric reactivity of 2D layered siloxene for high-energy-dense lithium-sulfur batteries

Lithium-sulfur batteries(LSBs)have emerged as promising power sources for high-performance devices such as electric vehicles.However,the poor energy density of LSBs owing to polysulfide shuttling and passivation has limited their further market penetration.To mitigate this challenge,two-dimensional(2D)siloxene(2DSi),a Si-based analog of graphene,is utilized as an additive for sulfur cathodes.The 2DSi is fabricated on a large scale by simple solvent extraction of calcium disilicide to form a thin-layered structure of Si planes functionalized with vertically aligned hydroxyl groups in the 2DSi.The stoichiometric reaction of 2DSi with polysulfides generates a thiosulfate redox mediator,secures the intercalation pathway,and reveals Lewis acidic sites within the siloxene galleries.The 2DSi utilizes the corresponding in-situ-formed electrocatalyst,the 2D confinement effect of the layered structure,and the surface affinity based on Lewis acid-base interaction to improve the energy density of 2DSi-based LSB cells.Combined with the commercial carbon-based current collector,2DSi-based LSB cells achieve a volumetric energy density of 612 Wh Lcell^(−1) at 1 mA cm^(−2) with minor degradation of 0.17%per cycle,which rivals those of state-of-the-art LSBs.This study presents a method for the industrial production of high-energy-dense LSBs.

Low-temperature synthesis of Fe_(2)(MoO_(4))_(3) nanosheets: A cathode for sodium ion batteries with kinetics enhancement

Sodium ion batteries (SIBs) are alternatives to lithium ion batteries (LIBs), and offer some significant benefits such as cost reduction and a lower environmental impact;however, to compete with LIBs, further research is required to improve the performance of SIBs. In this study, an orthorhombic Na super ionic conductor structural Fe_(2)(MoO_(4))_(3) nanosheet with amorphous-crystalline core-shell alignment was synthesized using a facile low-temperature water-vapor-assisted solid-state reaction and applied as a cathode material for SIBs. The obtained material has a well-defined three-dimensional stacking structure, and exhibits a high specific capacity of 87.8 mAh·g^(−1) at a current density of 1 C = 91 mA·g^(−1) after 1,000 cycles, which is due to the considerable contribution of extra surface-related reaction such as the pseudo-capacitive process. This material shows significantly improved cycling and rated behavior as well as enhanced performance under high- and low-temperature conditions, as compared to the same materials prepared by the conventional high-temperature solid-state reaction. This enhancement is explained by the unique morphology in combination with the improved kinetics of the electrochemical reaction due to its lower charge transfer resistance and higher sodium ion conductivity.