Flexible power sources and efficient energy storage devices with high energy density are highly desired to power a future sustainable community. Theoretically, rechargeable metal−air batteries are promising candidates for the next-generation power sources. The rational design of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts with high catalytic activity is critical to the development of efficient and durable metal−air batteries. Herein, we propose a novel strategy to mass synthesize nonprecious transition-metal-based nitrogen/oxygen codoped carbon nanotubes (CNTs) grown on carbon-nanofiber films (MNO-CNT-CNFFs, M = Fe, Co, Ni) via a facile free-surface electrospinning technique followed by in situ growth carbonization. With a combination of the high catalytic activity of Fe-catalyzed CNTs and the efficient mass-transport characteristics of 3D carbon fiber films, the resultant flexible and robust FeNO-CNT-CNFFs exhibit the highest bifunctional oxygen catalytic activities in terms of a positive half-wave potential (0.87 V) for ORR and low overpotential (430 mV @ 10 mA cm −2 ) for OER. As proof-of-concept, newly designed hybrid Li−air batteries fabricated with FeNO-CNT-CNFFs as air electrode present high voltage (∼3.4 V), low overpotential (0.15 V), and long cycle life (over 120 h) in practical open-air tests, demonstrating the superiority of the freestanding catalysts and their promising potential for the applications in fuel cells and flexible energy storage devices.

In situ synchrotron X-ray diffraction study of the synthesis of solid-electrolyte Li1+xAlxGe2−x(PO4)3 (LAGP) from the precursor glass reveals that an initially crystallized dopant poor phase transforms into the Al-doped LAGP at 800 °C.

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Polymer-based solid-state electrolytes are shown to be highly promising for realizing low-cost, high-capacity, and safe Li batteries. One major challenge for polymer solid-state batteries is the relatively high operating temperature (60-80°C), which means operating such batteries will require significant ramp up time due to heating. On the other hand, as polymer electrolytes are poor thermal conductors, thermal variation across the polymer electrolyte can lead to nonuniformity in ionic conductivity. This can be highly detrimental to lithium deposition and may result in dendrite formation. Here, a polyethylene oxide-based electrolyte with improved thermal responses is developed by incorporating 2D boron nitride (BN) nanoflakes. The results show that the BN additive also enhances ionic and mechanical properties of the electrolyte. More uniform Li stripping/deposition and reversible cathode reactions are achieved, which in turn enable all-solid-state lithium-sulfur cells with superior performances.

Developing inexpensive, noble metal-free, efficient, stable, and bifunctional electrocatalysts has attracted significant research interest in electrocatalysis and air battery-based energy storage devices. The fluorinated copper−manganese oxide (FCMO) is synthesized in an aqueous medium through a simple way using a hot plate and a fume hood. The FCMO catalyst is relatively inexpensive compared to Pt-, Ru-, and Ir-based catalysts, less hazardous than a Co-based catalyst, and at the same time, comparable with an Fe−Ni-based catalyst that has stable performance only in a basic medium. The FCMO is used in combination with carbon black as FCMO−carbon black by dispersing FCMO over carbon black to improve the electron transport efficiency. The FCMO catalyst and FCMO−carbon black show oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in both acidic and basic media with an impressive property of larger pH window stability with bifunctional performance. The ORR was found to be a two-electron process on both catalytic systems in both acidic and alkaline media. The FCMO−carbon black showed ORR (0.43 V) and OER (1.51 V) versus RHE in 0.5 M H 2 SO 4 . The onset potential of FCMO− carbon black was found to be an impressive 0.94 V versus RHE for the ORR and a relatively competitive OER of 1.54 V versus RHE in 0.1 M KOH. The FCMO−carbon black catalyst was also deposited on a conducting carbon cloth and used as an air cathode in a hybrid Li−air cell with 1.0 M LiOH as the electrolyte. The cell showed a stable cycling performance at room temperature for more than 80 h under a cycling current density of 0.08 mA cm −2 .