Cl-/SO32--Codoped Poly(3,4-ethylenedioxythiophene) That Interpenetrates and Encapsulates Porous Fe2O3 To Form Composite Nanoframeworks for Stable Lithium-Ion Batteries

Multifunctional Fe-S bonds assist poly(3,4-ethylenedioxythiophene) to enhance iron diselenide for ultra-long sodium storage lifetime

Transition metal selenides (TMS) have been used to prepare hundreds of electrode materials for ion batteries due to their superior theoretical capacity, but have been repeatedly limited by the sluggish reaction kinetics and the enormous volume change during the repeated charge/discharge process. Here, we report a facile strategy to fabricate organic-inorganic composites by engineering a unique chemical bonding interface between TMS and conductive polymers. For the first time, poly(3,4-ethylenedioxythiophene) (PEDOT) is utilized to encapsulate iron diselenide (FeSe2) nanoparticles by in situ polymerization, and the Fe-S bonds are meanwhile formed at the interface of FeSe2 and PEDOT. The experimental analysis demonstrates the stability of Fe-S bonds during the sodiation/desodiation process and after long cycling, which can serve as a "bridge" for fast charge transfer and also serve as a "rivet" to stabilize the composite structure. When used for sodium ion storage, the composite offers an exceptionally long lifetime of up to 17,000 loops at 10 A/g without capacity degradation. In addition, it delivers a high specific capacity of 490.4 mAh/g and retains 60 % when the current density is amplified 150 times. The assembled full cell also exhibits excellent cycling stability. This work will provide a feasible way to improve the metal oxide/sulfide/selenides for long-life ion batteries.

Enhancing Energy Storage via Confining Sulfite Anions onto Iron Oxide/Poly(3,4-Ethylenedioxythiophene) Heterointerface

Multiple oxidation-state metal oxide has presented a promising charge storage capability for aqueous supercapacitors (SCs); however, the ion insert/deinsert behavior in the bulk phase generally gives a sluggish reaction kinetic and considerable volume effect. Herein, iron oxide/poly(3,4-ethylenedioxythiophene) (Fe2O3/PEDOT) heterointerface was constructed and enabled boosted Faradaic pseudocapacitance by dual-ion-involved redox reactions in Na2SO3 electrolytes. The Fe2O3/PEDOT interface served as a "bridge" to couple electrode and anion SO32- and exhibited a strong force and stable bonding with SO32-, thus providing an additional Faradaic charge storage contribution for SCs. Significantly, the PEDOT-capsulated Fe2O3 nanorod array (Fe2O3@PEDOT) electrode presented a specific capacitance of 338 mF cm-2 at 1 mA cm-2 with 1 M Na2SO3 electrolyte, which was twice that of the pristine Fe2O3 nanorod electrode. The boosted interfaced Faradaic reaction of SO32- partially hindered the intercalation of Na+ in the Fe2O3 bulk phase, efficiently favoring the electrochemical stability.

Co-activated Conversion Reaction of MoO2:CoMoO3 as a Negative Electrode Material for Lithium-Ion Batteries

Extensive studies to develop high-capacity electrodes have been conducted worldwide to meet the urgent demand for next-generation lithium-ion batteries. In this work, we demonstrated a novel strategy to alter the lithiation mechanism of the transition metal oxide to increase the reversible capacity of the electrode material. A representative insertion-type negative electrode material, MoO₂, was modified by introducing a heterogeneous element (Co) to synthesize the solid solution of CoO and MoO₂ (CoMoO₃). CoMoO₃ exhibited a notably improved reversible capacity of 860 mA h g^-1, attributed to the conversion reaction, in contrast to MoO₂ that delivers 310 mA h g^-1, as it is limited by the insertion reaction. X-ray absorption spectroscopy and X-ray diffraction demonstrated that CoO is converted to Co and Li₂O, amorphizing the host structure, whereas the conversion of MoO₂ takes place subsequently. Furthermore, the superior initial Coulombic efficiency of CoMoO₃ (84.4%) to that of typical conversion materials is attributed to the highly conductive Co and MoO₂, which reinforce the electronic conductivity of the active particles. The results obtained from this study provide significant insights to explore high capacity metal oxides for the advanced lithium-ion batteries.

Inner-Stress-Optimized High-Density Fe3O4 Dots Embedded in Graphitic Carbon Layers with Enhanced Lithium Storage

The volume variation of electrode materials will lead to poor cyclability of lithium-ion batteries during the lithiation/delithiation process. Instead, inner-stress fragmentation is creatively used to change carbon-layer-capped Fe₃O₄ particles ∼30 nm in diameter into high-density Fe₃O₄ dots ∼4 nm in size embedded in ultrathin carbon layers. The optimized structure shows a remarkable 45.2% enhancement of lithium storage from 804.7 (the 10th cycle) to 1168.7 mA h g^-1 (the 250th cycle) at 500 mA g^-1, even retaining 1239.5 mA h g^-1 after another 550 cycles. The electrochemical measurements reveal the enhanced capacitive behavior of the high-density Fe₃O₄ dots@C layers, which have more extra active sites for the insertion/extraction of Li⁺ ions, confirmed by the differential capacity plots, leading to remarkably increased specific capacity during cycling. The restructured electrode also shows a superior rate capacity and excellent cycling stability (938.7 and 815.4 mA h g^-1 over 2000 cycles at 1000 and 2000 mA g^-1, respectively). X-ray photoelectron spectroscopy and transmission electron microscopy characterizations show that the optimized structure has stable structural and componential stability even at large rates. This work presents an MOF-guided synthesis of high-density Fe₃O₄-dots' anode material optimized by inner-stress fragmentation, showing a feasible route to design high-efficiency electrode materials.