Atomic-Scale Dynamics and Storage Performance of Na/K on FeF3 Nanosheet

Graphitized Carbon-Coated Iron Fluoride Nanocavities for Enhanced Kinetics of Multielectron Cathode Conversion Reactions

As for the conversion-type iron fluoride (FeF3) cathode material with multielectron reactions for lithium-ion batteries (LIBs), sluggish reaction kinetics and low electrical conductivity pose certain limitations for the long-lasting reversible conversion processes. Herein, the three-dimensional porous nitrogen-doped carbon matrix in situ anchoring FeF3 nanocavities coated by graphitized carbon (FeF3/GC) are rationally prepared. Through the Kirkendall effect, the low-temperature fluorination of NF3 enables the resultant hollow FeF3 nanoparticles to possess a large number of lithium storage cavities and outer graphitized carbon structure, further effectively buffering the expansion of volume. The FeF3/GC cathode delivers a superior discharge capacity of 504.2 mAh g-1 after 1200 cycles at 1000 mA g-1, with a capacity decay rate of only 0.01% per cycle. Even at a rate of 5000 mA g-1, the composite cathode still delivers a discharge capacity of 309.6 mAh g-1. Impressively, the existence of graphitized carbon and the short Li+ diffusion length ensure fast electron/ion transfer, which significantly enhances the conversion reaction kinetics. This study aims to provide a promising strategy for the efficiency enhancement of multielectron cathode conversion reactions for LIBs.

Reactant conversion-intercalation strategy toward interlayer-expanded MoS2 microflowers with superior supercapacitor performance

In order to avoid the complicated control and fussy procedure associated with foreign species and templates in conventional synthesis strategies, a simple reactant conversion-intercalation strategy is developed to synthesize interlayer-expanded MoS₂ (E-MoS₂) by employing ammonium thiocyanate converted from a thiourea reactant as intercalator. In this strategy, the thiourea plays a bifunctionality role as reactant and intercalator precursor to ensure in situ embedding into the interlayers of MoS₂ to expand the interlayer spacing. The optimal E-MoS₂ obtained presents superior supercapacitor performance with a specific capacity of 246.8 F g^-1 at 0.5 A g^-1 in 1 M Na₂SO₄ electrolyte in a three-electrode system, outperforming pristine MoS₂ prepared by a conventional hydrothermal method (42.5 F g^-1 at 0.5 A g^-1). Furthermore, a symmetric supercapacitor based on an E-MoS₂ electrode delivers a high specific capacity of 261.3 F g^-1 and energy density of 13.3 W h kg^-1 at 0.5 A g^-1, and excellent cycling life with 81.7% capacity retention after 3000 cycles at 2 A g^-1. Density functional theory calculations reveal that the NH₄⁺ and SCN^- can be effectively adsorbed on the surface to be inserted into the interlayers during the growth of MoS₂, resulting in an expanded interlayer spacing of 9.4 Å, and the favorable electrochemical performance stems from the large Na⁺ adsorption capacitance and low diffusion barrier of the E-MoS₂. This work offers a novel intercalation strategy that may be generally applicable to other layer-structured materials, shedding some light on the development of high-performance electrode materials via interface engineering for energy applications.