Carbon nanospheres for improved sodium-sulfur batteries

Sodium-sulfur batteries are promising electrical energy storage technologies that can serve as a key solution to intermittency problems and can be integrated with renewable forms of energy generation. An international research team has reported the synthesis of micro-mesoporous carbon nanospheres with continuous pore distribution as an efficient sulfur host for sodium-sulfur batteries. The work sheds new light on the progress of the sulfur cathode in sodium-sulfur batteries and provides a promising strategy for the viable design of other metal–sulfur batteries. Experiments at the CLAESS beamline in ALBA allowed determining the sulfur species during charge/discharge processes.

Solar and wind power are useful resources for energy generation but they are intermittent (at night or on cloudy days solar panels do not work, for example). Electrical energy storage technologies serve as a key solution to these intermittency problems and can be integrated with renewable forms of energy generation. Among these technologies, room-temperature sodium-sulfur (Na–S) batteries are deemed to be one of the most promising candidates, owing to their high theoretical energy density – the amount of energy they can store – and low cost. Nonetheless, this battery system suffers from a slow reaction rate at room temperature, which radically limits battery performance and makes difficult its practical commercialization.

An efficient strategy to deal with this challenge is the use of porous carbon material as a host to encapsulate molecular sulfur, significantly enhancing its conductivity. This system acts as the cathode of the battery, which is the electrode where reduction occurs. To make the battery work, sodium ions have to migrate from the anode to the cathode. However, in these systems, it is a challenge to provide fully accessible sodium ions that do not obstruct the sub-nanosized pores of the carbon host.

In a publication in the Advanced Materials journal, an international research team made up of Australian and Chinese institutions in collaboration with the ALBA Synchrotron has reported the synthesis of micro-mesoporous carbon nanospheres (MMPCS) with continuous pore distribution as an efficient sulfur host for sodium-sulfur batteries. This unique feature creates continuous channels that allow the movement of sodium ions without channels being obstructed. This enables a high conductivity, leading to fast sulfur reduction-oxidation reaction during the charge/discharge processes.

Read more on the ALBA website

Fe Cations Control the Plasmon Evolution in CuFeS2 Nanocrystals

Research on the synthesis of CuFeS2, an exciting semiconductor, outlines a method to verify its phase purity and investigate its properties.

Plasmonic semiconductor nanocrystals have become an appealing avenue for researching nanoscale plasmonic effects due to their wide spectral range (visible to infrared) and great tunability compared to traditional precious metal nanocrystals. CuFeS2 is an exciting semiconductor that has a prominent plasmon absorption band in the visible range (∼498 nm). In this work, the researchers determined the origin of the plasmonic behaviour in CuFeS2 by characterizing the nucleation and growth stages of the reaction through a series of ex situ and in situ probes (e.g., X-ray absorption spectroscopy and X-ray emission spectroscopy). They showed that the plasmon formation is driven by band structure modification from Fe(II) incorporation into the nanocrystals. Mixed oxidation state of Cu(I)/Cu(II) and Fe(II)/Fe(III) was observed.  Using these results, the researchers proposed a reaction mechanism for synthesis of CuFeS2 and outlined a method to verify the phase purity of the material.

Read more on the CHESS website