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Abstract Redox‐active organic compounds have attracted substantial attention as charge storage materials, owing to their high theoretical capacity. Herein, a two‐dimensional organic electrode material is prepared by using hydrothermally polymerized dopamine molecules on graphene nanosheets. Two‐dimensional polydopamine is employed as a positive electrode for storing alkali metal ions based on the surface redox reaction between oxygen functional groups and alkali ions. The two‐dimensional polydopamine positive electrodes deliver high capacities of 255 mAh g−1in Li cells, 150 mAh g−1in Na cells, and 124 mAh g−1in K cells at 0.1 A g−1, demonstrating a promising organic positive electrode for rechargeable alkali‐ion batteries.
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Abstract The energy and power performance of lithium (Li)‐ion batteries is significantly reduced at low‐temperature conditions, which is mainly due to the slow diffusion of Li‐ions in graphite anode. Here, it is demonstrated that the effective utilization of the surface‐controlled charge storage mechanism through the transition from layered graphite to 3D crumpled graphene (CG) dramatically improves the Li‐ion charge storage kinetics and structural stability at low‐temperature conditions. The structure‐controlled CG anode prepared via a one‐step aerosol drying process shows a remarkable rate‐capability by delivering ≈206 mAh g–1at a high current density of 10 A g–1at room temperature. At an extremely low temperature of −40 °C, CG anode still exhibits a high capacity of ≈154 mAh g–1at 0.01 A g–1with excellent rate‐capability and cycling stability. A combination of electrochemical studies and density functional theory (DFT) reveals that the superior performance of CG anode stems from the dominant surface‐controlled charge storage mechanism at various defect sites. This study establishes the effective utilization of the surface‐controlled charge storage mechanism through structure‐controlled graphene as a promising strategy to improve the charge storage kinetics and stability under low‐temperature conditions.
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Abstract Polydopamine, a functional coating material, is redox active as cathode materials for both Li‐ and Na‐ion batteries or hybrid capacitors. Here, a polydopamine coating onto 3D graphene framework is introduced through a simple hydrothermal process, during which graphene oxide serves not only as an oxidant for assisting the polymerization of dopamine, but also as a template for the conformal growth of polydopamine. High‐density films are fabricated by compressing the polydopamine‐coated graphene aerogels, which can be directly used as free‐standing and flexible cathodes in both Li‐ and Na‐cells. The compact electrodes deliver high capacities of ≈230 mAh g−1in Li‐cells and ≈211 mAh g−1in Na‐cells based on the total mass of electrodes. These compact electrodes also exhibit exceptional cycling stability and high rate performance due to the unique structure in which polydopamine is uniformly coated on the 3D structured graphene.
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Abstract Nanostructured graphene electrodes generally have a low density, which can limit the volumetric performance for energy storage devices. The liquid‐phase mild reduction process of graphene oxide sheets is combined with the continuous aerosol densification process to produce high‐density graphene agglomerates in the form of microspheres. The produced graphene assembly shows the cabbage‐like morphology with a high density of 0.75 g cm−3. In spite of such high density, the cabbage‐like graphene microspheres have narrow‐ranged mesopores and a high surface area. The cabbage‐like graphene microsphere exhibits both high gravimetric and volumetric energy densities due to the optimized microstructure, which shows a high gravimetric capacitance of 177 F g−1and volumetric capacitance of 117 F cm−3in supercapacitors. As a cathode for lithium‐ion capacitors, the cabbage‐like graphene delivers a reversible capacity of ≈176 mAh g−1. The stacking‐control approach provides a new pathway to control the microstructure of the graphene assembly and corresponding charge storage characteristics for energy storage applications.