Tailoring the Electrode Interface with Enhanced Electron Transfer for High-Rate Lithium-Ion Battery Anodes

Contact interface between the active materials and the current collector is essential for electron transfer rate and the mechanical properties of an electrode. In this study, various types of contacts between the active material (graphene sheets) and the metal current collector are created through different fabrication methods, and their impacts to the electrochemical performance are investigated. Intimate “sheet contact” is observed between graphene sheets and Ni foam after KOH <i>in situ</i> activation, which is believed to facilitate the electron transfer. The anode that is tailored to have “sheet contact” delivers a reversible capacity of 1457 mAh g^–1 at 0.1 C, which is higher than the electrode obtained by a commercial drop-casting method and comparable to most of the high-end graphene-based anodes. In addition, the anode delivers a high capacity of 173 mAh g^–1 with a short charging time of 56 s, indicating its promising use as a high-rate LIB anode

Interdiffusion Reaction-Assisted Hybridization of Two-Dimensional Metal–Organic Frameworks and Ti₃C₂T_<i>x</i> Nanosheets for Electrocatalytic Oxygen Evolution

Two-dimensional (2D) metal–organic framework (MOF) nanosheets have been recently regarded as the model electrocatalysts due to their porous structure, fast mass and ion transfer through the thickness, and large portion of exposed active metal centers. Combining them with electrically conductive 2D nanosheets is anticipated to achieve further improved performance in electrocatalysis. In this work, we <i>in situ</i> hybridized 2D cobalt 1,4-benzenedicarboxylate (CoBDC) with Ti₃C₂T_<i>x</i> (the MXene phase) nanosheets <i>via</i> an interdiffusion reaction-assisted process. The resulting hybrid material was applied in the oxygen evolution reaction and achieved a current density of 10 mA cm^–2 at a potential of 1.64 V <i>vs</i> reversible hydrogen electrode and a Tafel slope of 48.2 mV dec^–1 in 0.1 M KOH. These results outperform those obtained by the standard IrO₂-based catalyst and are comparable with or even better than those achieved by the previously reported state-of-the-art transition-metal-based catalysts. While the CoBDC layer provided the highly porous structure and large active surface area, the electrically conductive and hydrophilic Ti₃C₂T_<i>x</i> nanosheets enabled the rapid charge and ion transfer across the well-defined Ti₃C₂T_<i>x</i>–CoBDC interface and facilitated the access of aqueous electrolyte to the catalytically active CoBDC surfaces. The hybrid nanosheets were further fabricated into an air cathode for a rechargeable zinc–air battery, which was successfully used to power a light-emitting diode. We believe that the <i>in situ</i> hybridization of MXenes and 2D MOFs with interface control will provide more opportunities for their use in energy-based applications