Facile method for adjustable preparation of nano-Fe7S8 supported by carbon as the anode for enhanced lithium/sodium storage properties in Li/Na-ion batteries

Designing of trimetallic-phase ternary metal sulfides coupled with N/S doped carbon protector for superior and safe Li/Na storage

Traditional transition metal sulfides (TMSs) have shown favorable potentials in energy storage. Nevertheless, its further usage is plagued by the issues of particle breakage and large volume change. In this work, the nanostructured ternary TMSs coupled with N/S doped carbon protector (NiCoFe-S@NSC) is delicately designed via compositional regulation and spatial structure protection strategies. As lithium ion batteries anode, this electrode gives an impressive capacity of 995.7 mAh/g after running 1000 cycles at 1 A/g. More importantly, NiCoFe-S@NSC electrode still shows a discharge capacity of 221.94 mAh/g after running 20,000 cycles at 10 A/g, reflecting an extremely-low capacity decay rate of 0.0377 ‰ per cycle. As sodium ion batteries anode, a high initial discharge capacity of 896.4 mA h g^-1 can be found. Even after running 400 cycles at 5 A/g, the electrode still displays a reversible capacity of 334.5 mAh/g with outstanding coulombic efficiency above 98.0 %. Impressively, LiNi_xCo_yMn_1-x-yO₂//NiCoFe-S@NSC full cell gives incipient discharge/charge capacities of 186.89/240.18 mAh/g. Moreover, the discharge capacities for the following 100 cycles remain above 150 mAh/g. Thermal runaway tests also demonstrate the higher thermal safety of cells with NiCoFe-S@NSC electrode, accompanying with the promoted activation energy.

In-situ synthesis of Fe7S8 nanocrystals decorated on N, S-codoped carbon nanotubes as anode material for high-performance lithium-ion batteries

Fe₇S₈ has emerged as an attractive anode material for lithium-ion batteries (LIBs) due to its outstanding features such as low cost, high theoretical capacity, as well as environmental benignity. However, the rapid capacity fading derived from the tremendous volume change during the charging/discharging process hinders its practical application. Nanostructure engineering and the combination with carbonaceous material are essential to address this issue. In this work, Fe₇S₈ nanocrystals decorated on N, S-codoped carbon nanotubes (Fe₇S₈-NSC) were synthesized through a facile one-step pyrolysis of Fe-containing polypyrrole (PPy) nanotubes with sulphur powders under nitrogen atmosphere. When evaluated as anode of LIBs, Fe₇S₈-NSC demonstrates excellent cycling stability (718.8 mAh g^-1 at 100 mA g^-1 after 100 cycles) and superior rate ability (290.8 mAh g^-1 at 2000 mA g^-1). Moreover, Fe₇S₈-NSC shows a typical specific capacity recovery phenomenon, an extraordinary capacity of 744.4 mAh g^-1 at 2000 mA g^-1 after 1000 cycles can be achieved, which outperforms most of the Fe₇S₈-based anode materials reported before. The Fe₇S₈-NSC should be a promising anode material for high-performance LIBs.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO₂ layer is constructed on the surface of a metal-organic framework derived porous Fe₇ S₈ /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe₇ S₈ /C, the electroactive TiO₂ layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO₂ -modified Fe₇ S₈ /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO₂ -modified Fe₇ S₈ /C electrode delivers reversible capacity of 423.3 mA h g^-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO₂ coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Highly pseudocapacitive metal-organic framework derived carbon skeleton supported Fe-Ti-O nanotablets as an anode material for efficient lithium storage

A facile and effective method to fabricate highly pseudocapacitive electrodes of Fe-Ti-O@C has been proposed here. In this strategy, FeOOH crystals were firstly grown uniformly on the surface of Ti-based MOF (MIL-125) tablet substrates through a solution immersion method, and then converted to uniform carbon supported Fe-Ti-O composites by calcination under argon. The obtained Fe-Ti-O@C composites were first utilized as an efficient anode for lithium ion batteries with a high reversible capacity of 988 mA h g^-1 after 160 cycles at 200 mA g^-1. Such a superior lithium storage performance may be due to the synergistic effect of the Fe₃O₄ nanoparticles with a high capacity, FeTiO₃ nanocomposites with a nearly stable structure during the Li⁺ insertion/removal process, and the conductive carbon skeleton with a large surface area and porous structure. This work represents an important step forward in the fabrication of MOF-derived hybrids and enables transition metal oxides (TMOs) to have potential applications in energy storage systems.