Use of Nano Seed Crystals To Control Peroxide Morphology in a Nonaqueous Li–O₂ Battery

The high theoretical energy density of Li–O₂ batteries as required for electrification of transport has pushed Li–O₂ research to the forefront. The poor cyclability of this system due to incomplete Li₂O₂ oxidation is one of the major hurdles to be crossed if it is ever to deliver a high reversible energy density. Here we present the use of nano seed crystallites to control the size and morphology of the Li₂O₂ crystals. The evolution of the Li₂O₂ lattice parameters during <i>operando</i> X-ray diffraction demonstrates that the hexagonal NiO nanoparticles added to the activated carbon electrode act as seed crystals for equiaxed growth of Li₂O₂, which is confirmed by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) elemental maps also showing preferential formation of Li₂O₂ on the NiO surface. Even small amounts of NiO (∼5 wt %) particles act as preferential sites for Li₂O₂ nucleation, effectively reducing the average size of the primary Li₂O₂ crystallites and promoting crystalline growth. This is supported by first principle calculations, which predict a low interfacial energy for the formation of NiO–Li₂O₂ interfaces. The eventual cell failure appears to be the consequence of electrolyte side reactions, indicating the necessity of more stable electrolytes. The demonstrated control of the Li₂O₂ crystallite growth by the rational selection of appropriate nano seed crystals appears to be a promising strategy to improve the reversibility of Li–air electrodes

Magnetic Phase Transition in Spark-Produced Ternary LaFeSi Nanoalloys

Using the magnetocaloric effect in nanoparticles holds great potential for efficient refrigeration and energy conversion. The most promising candidate materials for tailoring the Curie temperature to room temperature are rare-earth-based magnetic nanoalloys. However, only few high-nuclearity lanthanide/transition-metal nanoalloys have been produced so far. Here we report, for the first time, the observation of magnetic response in spark-produced LaFeSi nanoalloys. The results suggest that these nanoalloys can be used to exploit the magnetocaloric effect near room temperature; such a finding can lead to the creation of unique multicomponent materials for energy conversion, thus helping toward the realization of a sustainable energy economy

<i>Operando</i> Nanobeam Diffraction to Follow the Decomposition of Individual Li₂O₂ Grains in a Nonaqueous Li–O₂ Battery

Intense interest in the Li–O₂ battery system over the past 5 years has led to a much better understanding of the various chemical processes involved in the functioning of this battery system. However, detailed decomposition of the nanostructured Li₂O₂ product, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure <i>operando</i> under realistic electrochemical conditions. Here, we report <i>operando</i> nanobeam X-ray diffraction experiments that enable monitoring of the decomposition of individual Li₂O₂ grains in a working Li–O₂ battery. Platelet-shaped crystallites with aspect ratios between 2.2 and 5.5 decompose preferentially via the more reactive (001) facets. The slow and concurrent decomposition of individual Li₂O₂ crystallites indicates that the Li₂O₂ decomposition rate limits the charge time of these Li–O₂ batteries, highlighting the importance of using redox mediators in solution to charge Li–O₂ batteries