Well-dispersed MnO-quantum-dots/N-doped carbon layer anchored on carbon nanotube as free-standing anode for high-performance Li-Ion batteries

A mild reduction of Co-doped MnO2 to create abundant oxygen vacancies and active sites for enhanced oxygen evolution reaction

Efficient and non-precious-metal-based catalysts (e.g., manganese-based oxides) for the oxygen evolution reaction (OER) remain a substantial challenge. Creation of oxygen vacancies of manganese-based oxides with the aim to enhance their intrinsic activities is rarely reported, and there is a critical requirement for a mild and facile synthesis strategy to create abundant oxygen vacancies on manganese-based oxides. Herein, Co-doped MnO₂ nanowires were reduced by NaBH₄ solution at room temperature; then, MnCo₂O_4.5 nanosheets with abundant oxygen vacancies and active sites were formed on the surface of Co-doped MnO₂ nanowires. Benefiting from the reduction strategy, the fabricated hierarchical Co-doped-MnO₂@MnCo₂O_4.5 nanowire/nanosheet nanocomposites exhibit higher catalytic activity (an overpotential of 250 mV at a current density of 10 mA cm^-2 in 1.0 M KOH solution) than pristine Co-doped MnO₂ nanowires. The calculated TOF of Co-doped-MnO₂@MnCo₂O_4.5 is 0.034 s^-1 at the overpotential of 300 mV, which is 136-fold higher than that of Co-doped-MnO₂. The excellent OER performance was attributed to the synergistic advantages of abundant oxygen vacancies and active sites over the hierarchical nanowire-nanosheet architectures.

Flexible MnO nanoparticle-anchored N-doped porous carbon nanofiber interlayers for superior performance lithium metal anodes

The mounting requirements for electric apparatus and vehicles stimulate the rapid progress of energy storage systems. Lithium (Li) metal is regarded as one of the most prospective anodes for high-performance cells. However, the uneven dendrite growth is one of the primary conundrums that hampers the use of the Li metal anode in rechargeable Li batteries. Achieving even Li deposition is crucial to solve this concern. In this study, a stable interlayer based on electrospun flexible MnO nanoparticle/nitrogen (N)-doped (polyimide) PI-based porous carbon nanofiber (MnO-PCNF) films was effectively prepared via electrospinning and in situ growth of MnO to reduce the growth of Li dendrites. It is revealed that the attraction of implanted MnO towards Li, the lithiophilic nature of N dopants and the capillary force of porous architectures are beneficial to the preeminent Li wettability of the MnO-PCNF interlayer. Furthermore, the wettable, stable and conductive structure of the MnO-PCNF interlayer can be retained well, offering rapid charge transfer to Li redox reactions, reduced local current density during the cycling process and homogeneous distribution of deposited Li. Consequently, anodes with MnO-PCNF interlayers can relieve the volume change and inhibit the growth of Li dendrites, demonstrating a remarkable lifetime for lithium metal cells at high current.

Polymerization inspired synthesis of MnO@carbon nanowires with long cycling stability for lithium ion battery anodes: growth mechanism and electrochemical performance

Manganese-based transition metal oxides are regarded as one kind of high capacity and low cost anode material for Li-ion batteries. To overcome the challenges of poor electrical conductivity and large volumetric expansion during the charging-discharging process of MnO, we here synthesize MnO@carbon (MnO@C) nanowires via the polymerization inspired in situ growth of [Mn-NTA] (NTA = nitrilotriacetic acid) precursor nanowires with a subsequent heat treatment process. The growth mechanism of [Mn-NTA] precursor nanowires was studied. The morphology of the precursor nanowires depended largely on the molar ratio of MnCl2 to NTA reactants. At a molar ratio of 2, the length of the [Mn-NTA] nanowires reached up to more than 140 μm. Furthermore, the as-synthesized MnO@C nanowires were integrated with a very low content of reduced graphene oxide (rGO) to prepare a self-standing paper-like MnO@C/rGO anode for lithium ion batteries without a binder. The MnO@C/rGO anode showed a unique structure with one-dimensional porous MnO nanowires hierarchically encapsulated by a conductive carbon framework. As a result, the self-standing electrode achieved a high capacity of 1368 mA h g-1 after 100 cycles at a current density of 100 mA g-1 and prominent cycling stability with a capacity of 689.9 mA h g-1 even after 1700 cycles at 2000 mA g-1.